There are a number of applications for gas-depolarizable galvanic cells such as zinc-air cells where it is desired to operate the cell and thereby to draw electrical power therefrom only intermittently and at low to medium current flow rates. Typical applications of such operation of gas-depolarizable or metal-air cells may include transistor radios, wall clocks, photographic strobe lights, and the like. In all such circumstances the current flow rate and demand therefor from the cell are quite low when compared, say, to flashlight operation, radio transmitters and the like. In general, it is desirable to restrict the gas flow communication to the gas-depolarizable cathode of the cell, thereby restricting water vapour access to or egress from the cell. Indeed, in some circumstances, it may be desirable to control the limiting current which may be drawn from the cell at its rated terminal voltage.
The major concern, however, is to assure a long operable life for a gas-depolarizable galvanic cell in low rate applications and with intermittent operation, particularly by precluding either moisture loss from the alkaline electrolyte of the cell in low relative humidity ambient conditions, or excessive water vapour absorption by the alkaline electrolyte of the cell at high relative humidity ambient conditions. Obviously, if the alkaline electrolyte is permitted to lose its moisture content and therefore to dry out, the cell may become inoperable. Similarly, if there is too much water vapour influx and absorption by the electrolyte, the physical dimensions of the cell may be altered in that it may be caused to bulge and thereby to leak electrolyte from the cell.